The most frigid spot known on Earth’s surface is at the Vostok Ice Station in Antarctica, where in 1989 the temperature hit –128.6 degrees Fahrenheit. It was so cold that when scientists there poured water from a kettle, the water froze before it hit the ground. At the other extreme is El Azizia, Libya, where the hottest temperature—136° F—was recorded in September 1922. High in the atmosphere or deep underground, temperatures are even more extreme. In the noctilucent clouds that form 50 miles above the North and South poles, temperatures fall as low as –220° F. And in Earth’s solid iron inner core, 4,000 miles beneath us, temperatures may reach 13,000° F—hotter than the surface of the sun. In the laboratory, scientists can generate hotter and colder temperatures. Temperature is just a measure of the kinetic energy in a sample of moving atoms. Thermal motion disappears at absolute zero: –459.67° F, or zero K on the Kelvin scale. Absolute zero cannot be reached experimentally, but scientists have cooled small samples of atoms to just one ten-billionth of a degree above absolute zero. Meanwhile, fusion researchers in Japan and the United States have produced temperatures above 900 million ° F in plasmas of deuterium and tritium, which are isotopes of hydrogen. The plasmas are confined by magnetic fields because no physical container could withstand such heat.